For antennas and planar circuits, where you typically define one or more ports, you usually use lumped sources. A lumped source is indeed a gap discontinuity that is placed on the path of an electric or magnetic current flow, where a voltage or current source is connected to inject a signal. Gap sources are placed across metal or slot traces. Probe sources are placed across vertical PEC vias. A de-embedded source is a special type of gap source that is placed near the open end of an elongated metal or slot trace to create a standing wave pattern, from which the scattering [[parameters]] can be calculated accurately. To calculate the scattering characteristics of a planar structure, e.g. its radar cross section (RCS), you excite it with a plane wave source. Short dipole sources are used to explore propagation of points sources along a layered structure. Huygens sources are virtual equivalent sources that capture the radiated electric and magnetic fields from another structure possibly in another [[EM.Cube]] computational module and bring them as a new source to excite your planar structure.
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A rectangle strip object on a PEC or conductive sheet trace can be regarded as a strip transmission line that carries electric currents along its length (local X direction). The characteristic impedance of the line is a function of its width (local Y direction). A gap source is placed somewhere along the length and across the width of such a rectangle strip object, thus creating an infinitesimally narrow gap at its location. In this case, the gap source represents an ideal voltage source in series with a lumped impedance that is connected across the gap to excite the strip transmission line. When the impedance is zero, the gap acts like an ideal lumped source and creates a uniform electric field across the gap. The source pumps electric current into the line. If the voltage source is shorted (having a zero amplitude), then the gap acts like a series lumped element on the transmission line.
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A rectangle strip object on a PMC trace can be regarded as a slot transmission line on an infinite PEC ground plane that carries a magnetic current along its length (local X direction). The characteristic impedance of the slot line is a function of its width (local Y direction). A slot gap source is placed somewhere along the length and across the width of the rectangle strip object on a PMC trace and creates an infinitesimally narrow gap at its location. In this case, the slot gap source represents an ideal current source with a shunt lumped admittance that is connected across the slot to excite the slot transmission line. When the admittance is zero, the gap acts like an ideal current filament, which creates electric fields across the slot, equivalent to a magnetic current flowing into the slot line. If the current source is open (having a zero amplitude), then the gap acts like a shunt (parallel) lumped element on the slot line. As you will see later, a coplanar waveguide (CPW) can be realized using two parallel slot lines with two aligned, collocated gap sources.
[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Planar MoM Source Types]]'''.